Thinner people have more 'brown fat' than heavier people; may help in weight loss

By ROSEMARY BLACK

|DAILY NEWS STAFF WRITER|

Apr 09, 2009 | 3:36 PM

Overweight people have more white fat than calorie-burning brown fat, according to a study published in the New England Journal of Medicine. (Wigglesworth/AP)

Feeling fat? If yours is brown, chances are you're not as chubby as you think you are. Scientists have discovered that thinner people have more "brown fat" than heavier people. Unlike regular white fat, brown fat actually burns calories for heat -- at least in mice.

In addition to thin grownups having more of it than fatter ones, younger people have more than older people and women have more than men. People taking beta blockers for high blood pressure had less brown fat than those that didn't.

The research, from the Joslin Diabetes Center in Boston, involved nearly 2,000 patients. Scientists found that almost all grownups have small brown fat blobs that can burn mega calories when activated by cold - as in, when someone is in a 61-degree room.

"The thing about brown fat is that it takes a very small amount to burn a lot of energy," Dr. C. Ronald Kahn, head of the section on obesity and hormone action at the Joslin Diabetes Center, told the Times.

What makes the fat brown is that it is filled with iron-containing mitochondria, which the Times calls "tiny energy factories of cells," which impart a brownish-red color to the fat. In grownups, brown fat mostly shows up in the upper back, side of the neck and along the spine, while infants mostly carry brown fat as a sheet of cells on their backs, the Times reported. Mice, which mostly have brown fat between their shoulder blades, lost 14 percent of their weight when they spent a week in a cold room - even though they scarfed down a high-fat diet.

Researchers were able to find the brown fat in humans with PET-CT scans. The PET scans pointed to the areas where cells were burning glucose, and the CT scans showed that it was fat.

Nearly 2,000 people had scans for various reasons, and brown fat showed up in 7.5 percent of women and 3 percent of men. Kahn said that was actually an underestimate because the people who were scanned had not activated their brown fat by getting cold.

Though there's currently no way you can simply turn on your brown fat-making cells and switch off your white fat-making cells, the study is intriguing because some day, scientists may discover a safe way to switch on people's brown fat and allow them to shed pounds by burning off more calories. Unfortunately, it's not known yet whether people would shed pounds as mice do when their brown fat is activated.

But in the meantime, you've got the perfect excuse for chilling out this summer by running your AC on high.